Well perforating apparatus

Abstract

The apparatus comprises an elongated support (22) having a series of flat-faced portions and explosive charges (23) mounted perpendicular to the flat faces. Detonating cords are connected to the charges to fire them. Each portion of the support has two closely spaced attachment holes adapted to receive respectively the rear parts of the two charges mounted in opposite directions on each face of this section. The support is made up of a tube flattened transversely so as to form the flat-faced portions. Spacers are disposed between the charges and the support for casings of large diameter. The cases of the charges comprise a cover made of ceramic material and an extruded steel body which tends to flare out when the explosive is detonated rather than being broken into pieces.

We claim: 
     
       1. In a well perforating apparatus including an elongated support, means forming longitudinally spaced attachment holes in the support, explosive charges having sealed cases fixed to the support in the attachment holes wherein each charge case comprises a metallic body member of sufficient strength for attachment to said support and detonating means connected to said charges to fire them, the improvement comprising: (a) means on said support forming a series of angularly offset flat-faced support portions around and in the longitudinal direction thereof,   (b) means on each of said support portions forming pairs of the longitudinally spaced attachment holes therein with a distance between the centers of each hole within the pair being smaller than the maximum diameter of a charge perpendicular to its axis, each of said attachment holes being configured to support a charge with the axis of the charge substantially perpendicular to said support portion flat faces,   (c) rear parts in the charge cases adapted for engaging said charge cases in said attachment holes such that two charges are fixed on each of said support portions with the axes of said two charges oriented in opposite radial directions, and   (d) a cover member for each of said charge cases made of brittle material for breaking into small size debris after the explosion of the charge, wherein said metallic body is made of extruded steel having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of said body opens under the effect of the explosion of the charge while remaining attached by the rear part of the charge to said support after the explosion.   
     
     
       2. The apparatus of claim 1 wherein said charge case cover member is made of ceramic. 
     
     
       3. In a well perforating apparatus including an elongated support, means forming longitudinally spaced attachment holes in the support, explosive charges having sealed cases fixed to the support in the attachment holes and detonating means connected to said charges to fire them, the improvement comprising: (a) means on said support forming a series of angularly offset flat-faced support portions around and in the longitudinal direction thereof,   (b) means on each of said support portions forming pairs of the longitudinally spaced attachment holes therein with a distance between the centers of each hole within the pair being smaller than the maximum diameter of a charge perpendicular to its axis, each of said attachment holes being configured to support a charge with the axis of the charge substantially perpendicular to said support portion flat faces,   (c) rear parts in the charge cases adapted for engaging said charge cases in said attachment holes such that two charges are fixed on each of said support portions with the axes of said two charges oriented in opposite radial directions, and   (d) removable spacers configured for insertion between the charges and said support for reducing the clearance between the front parts of the charges and the well casing to improve the perforation of boreholes cased with large diameter well casings.   
     
     
       4. The apparatus of claim 3 further comprising several types of removable spacers of different predetermined lengths for boreholes having well casings of different diameters. 
     
     
       5. The apparatus of claim 6 wherein the rear parts of each charge include means forming a cord passage slot for affording the passage of a detonating cord, and wherein each of said spacers further comprises an annular part adapted to surround the rear part of the body of a charge and , inside this annular part, a transverse part adapted to engage in said cord passage slot when the rear part of a charge is placed in the spacer, in order to reduce the volume of fluid inside the spacer, while ensuring proper application of the cord against the charge body. 
     
     
       6. The apparatus of claim 5 wherein said annular part of each spacer has a reinforced thickness. 
     
     
       7. A well perforating apparatus comprising: (a) an elongated support,   (b) means forming longitudinally spaced attachment holes in the support,   (c) explosive charges having sealed cases fixed to the support in the attachment holes, each charge case including a metallic body member of sufficient strength for the attachment to the support and being made of extruded steel having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of said body opens under the effect of the explosion of the charge while remaining attached by the rear part of the charge to said support after the explosion, and a cover member made of a brittle ceramic material for breaking into small size debris after the explosion of the charge,   (d) means on said support forming a series of angularly offset flat-faced support portions around and along the longitudinal direction thereof, each two successive flat-faced sections being oriented with perpendicular radial directions so as to afford the positioning of explosive charges oriented along four radial directions with 90 degrees offsets therebetween,   (e) means on each of said support portions forming said longitudinally spaced attachment holes therein in pairs with a distance between the centers of each pair smaller than the maximum diameter of a charge perpendicular to its axis, said attachment holes being configured to support the charges with axes of the charges being substantially perpendicular to said support portion flat faces,   (f) rear parts in the charge cases for engaging the charges in said attachment holes such that two charges are fixed on each of said support portions with the axes of said two charges oriented in opposite radial directions,   (g) detonating means including two detonating cords connected respectively to a first series of charges consisting of a charge of each portion and to a second series of charges consisting of the other charge of each portion, an explosive relay connected to fire the two detonating cords simultaneously, and a detonator operated electrically to set off said explosive relay for firing said two detonating cords to fire the respective series of charges connected thereto, and at least one additional explosive relay spaced longitudinally along the support each of said additional relays being connected to the two detonating cords to maintain the simultaneous detonation of the two detonating cords,   (h) means in the rear parts of each charge case forming a detonating cord passage slot for the passage of a detonating cord and positioned so that, after attaching a charge case on a support portion, the detonating cord for firing the respective said charge is disposed along the support side directed toward the front of said charge,   (i) means in each attachment hole forming at least one flat part thereon to prevent the rotation of the charge engaged in this attachment hole, and   (j) a plurality of removable spacers, some of different predetermined lengths for boreholes having well casings of different diameters, each such spacer being configured for insertion between the charges and said support for reducing the clearance between the front parts of the charges and the well casing thereby affording improved perforation within boreholes cased with large diameter well casings, and each of said spacers having an annular part of reinforced thickness adapted to surround the rear part of the body of a charge and, inside this annular part, a transverse part adapted to engage in said cord passage slot when the rear part of a charge is placed in the spacer, in order to reduce the volume of fluid inside the spacer while ensuring proper application of the cord against the charge body.   
     
     
       8. A method for perforating a well with a high charge density, comprising: (a) lowering into the well a high charge density perforation apparatus having sealed explosive charge cases with reduced diameter rear parts inserted and fixed, with the axes thereof oriented in opposite radial directions, into respective pairs of longitudinally spaced attachment holes formed in a series of flat-faced support portions on and angularly offset around a support along the longitudinal direction thereof, the distance between the centers of the holes in each pair being smaller than the maximum diameter of a charge perpendicular to its axis, and the holes being configured to support the charges with axes substantially perpendicular to the support portion flat faces, wherein the charge cases are formed by extruding a steel body member of sufficient strength for attachment to said support and of a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of the body opens under the effect of explosion of the charge while remaining attached to the support by the rear part of the charge case and wherein the clearance between the front parts of the charges and the well casing is reduced by inserting removable spacers between the charges and the support, for better perforating boreholes cased with large diameter well casings, and   (b) firing the charges.   
     
     
       9. A method for perforating a well with a high charge density, comprising: (a) lowering into the well a high charge density perforation apparatus having sealed explosive charge cases with reduced diameter rear parts inserted and fixed, with the axes thereof oriented in opposite radial directions, into respective pairs of longitudinally spaced attachment holes formed in a series of flat-faced support portions on and angularly offset around a support along the longitudinal direction thereof, the distance between the centers of the holes in each pair being smaller than the maximum diameter of a charge perpendicular to its axis, and the holes being configured to support the charges with axes substantially perpendicular to the support portion flat faces, and wherein the charge cases are formed by extruding a steel body member of sufficient strength for attachment to said support and having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of the body opens under the effect of the explosion of the charge while remaining attached to the support by the rear part of the charge case, wherein a detonating cord is connected to each charge through a cord passage slot in the rear parts thereof, and wherein a transverse part of the spacer is engaged in the slot and the rear part of the charge is placed in the spacer to reduce the volume of fluid inside the spacer while ensuring proper application of the cord against the charge body, and   (b) firing the charges.   
     
     
       10. A method for perforating a well with a high charge density, comprising: (a) lowering into the well a high charge density perforation apparatus having sealed explosive charge cases with reduced diameter rear parts inserted and fixed, with the axes thereof oriented in opposite radial directions, into respective pairs of longitudinally spaced attachment holes formed in a series of flat-faced support sections on and angularly offset around a support along the longitudinal direction thereof, the charge cases being formed by extruding a steel body member of sufficient strength for the attachment and having a better breaking resistance in the direction of the charge axis than perpendicular to this axis so that the major part of the body opens under the effect of the explosion of the charge while remaining attached to the support by the rear part of the charge case, the distance between the centers of the holes in each such pair of holes being smaller than the maximum diameter of a charge perpendicular to its axis, the holes being configured to support the charges with axes substantially perpendicular to the support section flat faces, the clearance between the front parts of the charges and the well casing being reduced by inserting removable spacers between the charges and the support, for better perforating boreholes cased with large diameter well casings, the charges being connected for firing by two detonating cords connected respectively to a first series of charges consisting of a charge of each section and a second series of charges consisting of the other charge of each section, each detonating cord being connected to each charge through a cord passage slot in the rear parts thereof, and a transverse part on the spacer being engaged into the slot while placing the rear part of the charge in the spacer to reduce the volume of fluid inside the spacer while ensuring proper application of the cord against the charge body, and an electrically operated detonator being connected to the two detonating cords for firing them, and   (b) firing the charges by means of the electrically operated detonator and the detonating cords.